1. Field of the Invention
The invention relates to a process for detecting and correcting a change in the fiber orientation cross-direction profile of a paper or cardboard web in the manufacturing process of a paper or cardboard machine. Furthermore, the invention relates to a device for detecting and correcting a change in the fiber orientation cross-direction profile in the manufacturing process.
2. Discussion of Background Information
In the manufacture of a paper or cardboard web, there are a large number of interfering factors in the manufacturing process, which can negatively influence the web properties of the paper or cardboard web with regard to its uniformity over the width of the machine used in the manufacture of the web. These interfering factors include, for example, temperature fluctuations, pressure fluctuations, and manufacture tolerances, but also include changes to the machine due to constant wear. Two significant web properties that influence the quality of the paper produced are the desirable, mostly uniform mass distribution of the paper and the desirable, mostly uniform orientation of the fibers in the paper.
The uniform mass distribution assures a favorable basis weight cross-direction profile and a corresponding uniform thickness of the paper layer, while a uniform and correctly aligned fiber orientation has a significant influence on the breaking length ratio, the "curl" of copier papers, and also the running properties of roll papers. In this connection, reference is made to the publications by Robert A. Braun, APPITA 1995, 229 to 234; Scott B. Pantaleo, TAPPI Proceedings, 1994, 259 to 264, and Wochenblatt fur Papierfabrikation [Weekly of Paper Manufacturing] 123, February 1995, No. 4, pp. 121 to 126.
For detecting and influencing a web properties profile, such as the basis weight crossdirection profile of a paper or cardboard web, patent document DE 35 35 849 has disclosed measuring the basis weight cross-direction profile of a paper web and, in accordance with the desired change, altering the width of the outlet gap of a headbox at particular locations on the web width so that the flow rate of the stock suspension correspondingly changes locally. The change in the flow rate of the stock suspension, with an even concentration over the width of the web manufacturing machine, influences the quantity of solids at locations on the web and consequently produces an adjustment of the basis weight cross-direction profile.
Patent document DE 40 19 593 A1 discloses a device and a process for regulating the basis weight profile of the web. In this process, when there is a variation of the basis weight profile of the paper web at a particular location on the web width, the concentration of the stock suspension flow should be changed at the particular location. In order to achieve this, a proposal has been made to section the headbox, at least partially, over the width of the machine and to charge the headbox with individually adjustable concentrations with the aid of regulated sectional flows. The individual adjustment of the concentration of the respective sectional flows is carried out by regulating the influx ratios of two individual flows with constant, but different concentrations. The differing content of the sectional flows as regards fibrous material, such as ash and other additives, produces a change in the basis weight at the corresponding location on or across the web width.
Regulating processes for sectional adjustment of headboxes have been disclosed, for example, in patent documents DE 42 38 037 and DE 40 05 281. In these regulating processes, the basis weight cross-direction profile in the paper web is respectively measured and, in accordance with the changes in the basis weight cross-direction profile from the ideal state, the corresponding actuators in the headbox are adjusted in order to achieve the desired basis weight cross-direction profile.
A similar control/regulation device as well as a process for regulating the basis weight cross-direction profile and the fiber orientation cross-direction profile has been disclosed by patent document DE 42 39 845. This document provides for embodying the headbox likewise, at least partially, in sections and influencing the paper stock suspension in its consistency and/or fiber orientation in the individual sections by a supply of dilution water or other fluids in order to regulate the corresponding cross-direction profile. This document , though, does not indicate how the change in a fiber orientation cross-direction profile can be measured.
Furthermore, reference is made to patent document DE 196 34 997, which describes a regulating device with a number of measurement sensors and a process for regulating different web property profiles. The measurement process described in this document, by a number of measurement sensors for determination of the web thickness, describes a measurement process for determining separate basis weight cross-direction profiles and basis weight longitudinal direction profiles in a paper web, wherein the basis weight crossdirection profiles determined by this procedure can be represented free of components of the basis weight longitudinal direction profile. A similar process has also been disclosed by DE 20 19 975.
Patent document DE 196 34 996, which discloses a sectional stock density-regulated headbox with a paper stock consistency regulation. Likewise, patent documents DE 42 11 291 and DE 42 11 290 disclose a sectional stock density regulation of a headbox, with a single valve per section with uniform volume flow. Patent documents DE 40 19 593 and DE 41 12 347 disclose a stock density regulation and volume flow regulation for a sectioned headbox with two valves per section.
The disclosure of the above-discussed documents is expressly incorporated by reference herein in their entirety.
The above-discussed background information does, in fact, represent a number of possibilities with which a fiber orientation cross-direction profile of a paper web can be influenced by the headbox, but none of the foregoing documents explain how a change in the fiber orientation cross- direction profile or the fiber orientation cross-direction profile itself can be measured "on line" during the operation of the paper machine that forms the web. The currently known measuring methods of the fiber orientation cross-direction profile cannot be carried out "on line" or else would require an extremely high degree of expense.
There is the problem, therefore, that before a proper continuous regulation of the fiber orientation cross-direction profile can be carried out in an operating paper machine, a reasonably priced process is required for detecting a change in a fiber orientation crossdirection profile.